Wind energy as a kind of clean, non-polluting and renewable energy attracts considerable attention. After many years developing, the proportion of wind power is increasing year by year, while the capacity of a single wind generator gets bigger and bigger. The capacity of a converter being as a main component of a wind generator increases rapidly, for example, the capacity of foreign mainstream models from 500˜1000 KW in 2000 year to 2˜3 MW in 2009 year, currently being developed to 8˜10 MW; the capacity of domestic mainstream models from 600˜1000 KW in 2005 to 850˜2000 KW in 2009, currently being developed to 6 MW.
Typically, a converter includes a rectifier circuit and an inverter circuit. In the inverter circuit or the rectifier circuit, it is required to perform an inverting conversion from a direct current (DC) to an alternative current (AC), or a rectifying conversion from an AC to a DC, so as to output an AC or a DC. As the capacity of a single converter increases, it is required to increase the capacity of power modules (power stack) constituted by large power components. Therefore, due to cost and semiconductor device manufacturing process level, it requires that power components (for example, IGBTs, i.e., Insulated Gate Bipolar Transistors) are used in parallel to meet the design output requirements.
For parallelling IGBTs, an important issue is how to equalizing current among the components. Good current equalizing can improve component utilization and save cost, as well as improve system reliability. How to design AC busbars and DC busbars for parallelled IGBTs critically affects the current equalizing, and the smaller the parasitic inductance of each parallel branch is, the better current equalizing effect is.
As shown in FIG. 1, in a conventional arrangement manner, AC busbars and DC busbars are disposed symmetrically, wherein power modules 1 and 2 are connected in parallel, positive and negative DC terminals of the power module 1 and the power modules 2 are connected to DC terminals (for example, the positive and negative terminals of a bus capacitor C) via the DC busbar, and AC terminals of the power modules 1 and 2 are connected to a load (not shown in FIG. 1) via the AC busbars. In FIG. 1, L1, L2, L4 and L5 represent parasitic inductances of the DC busbars, and L3 and L6 represent parasitic inductances of the AC busbars. By way of the arrangement of FIG. 1, it can be realized that L1+L2=L4+L5 and L3=L6, thereby obtaining a good current equalizing. However, this arrangement manner requires symmetrically design of AC busbars, resulting in large size and high cost of copper busbars and high requirement for line-feeding manner of the copper busbars. In addition, it is difficult to install these symmetrical copper busbars, which does not facilitate system design.
Another traditional arrangement manner is shown in FIG. 2. In the arrangement shown in FIG. 2, an AC busbar as a common AC busbar is directly connected to AC terminals of the IGBTs, without considering whether L3 and L6 are equal. A whole assembly of AC busbars and DC busbars in FIG. 2 is shown in FIG. 3, where arrows indicate inflow directions of current. As shown in FIG. 3, a DC busbar 3 is respectively connected to the positive or negative DC terminals of the power module 1 and the power module 2, and an AC busbar 4 is connected to the AC terminals of the power modules 1 and 2 and a load (not shown in FIG. 2), wherein a parasitic inductance of the AC busbar 4 between the power modules 1 and 2 in FIG. 3 can be equivalent to L6 in FIG. 2, a parasitic inductance of the AC busbar 4 between the AC output terminal of the power module 1 and the load is equivalent to L3 in FIG. 2. From FIG. 2 and FIG. 3, it can be seen that, although this design is simple and the installation is relatively easy in comparison with the previously mentioned manner, the parasitic inductances caused by the AC busbar with respect to power modules 1 and 2 are different, resulting in a dissatisfactory current equalizing effect.
Therefore, the arrangements in the prior art either have a simple structure while having a poor current equalizing effect, or have a good current equalizing effect while having a complicated design, large volume and stiff line-feeding manner, and thus affecting the overall system design.